Vibrations are caused in the normal operation of various types of rotating machinery, for example aircraft turbine engines and other turbomachinery, rotating devices deployed on-board satellite and other spacecraft for attitude adjustment purposes, such as control moment gyroscopes and reaction wheels, automobile turbochargers, generators and pumps, and other rotating machinery. When machinery rotates, there can be loads or forces created due to imbalances in the rotation, referred to as synchronous responses. These forces can be amplified when the rotating machinery transitions a critical angular velocity. In addition, rotating machinery can experience non-synchronous responses due to de-stabilizing forces, such as a change in direction of travel (directional acceleration) or jarring forces such as air turbulence or uneven pavement, among others. These forces (synchronous and non-synchronous) can result in vibration of the overall system associated with the rotating machinery. Such vibrations have a detrimental effect on both the performance of the machinery and the comfort of persons who may be present on-board a vehicle associated with the rotating machinery (e.g., airplane, helicopter, automobile, etc.).
Jet engines, particularly turbofan engines, contain a number of components that rotate about a central axis. Because vibrations can introduce eccentricity in the rotation, vibrations can degrade the performance of the engine. This degraded performance can be manifest as a decrease in thrust, which can, in turn, increase the length of a flight as well as the fuel required. The vibrations also can travel through the frame of the aircraft to compartments containing passengers and operators. While not harmful, vibrations can be an unpleasant aspect of travel for the occupants.
The most common approach to reducing the impact of vibrations on rotating machinery components is to provide a squeeze film damper (SFD). Typically, a bearing rotatably supports a shaft in the machinery, such as a rotor shaft in the example of a jet engine. The bearing is, in turn, supported by a SFD. The SFD damps vibrations from the rotor by providing a constant flow of oil to an annular chamber surrounding the bearing. The oil film can be squeezed through one or more exit channels when the bearing moves from its central position as a result of rotor shaft eccentricity. SFDs are not ideal because they offer sub-optimal damping characteristics while still requiring oil and maintenance. Additionally, the use of SFDs requires tolerancing for positioning of the rotor shaft and bearings that can introduce variations in the center of rotation of the shaft, further reducing performance.
Additionally, many common approaches to reducing the impact of vibrations on rotating machinery provide isotropic vibrational damping support. That is, the mounting assembly includes supports and dampers configured to provide the same degree of damping support in all directions relative to the rotation of the machinery. Referring to FIG. 1, an exemplary isotropic vibration mounting assembly is shown including three identically configured, generic vibration isolators 10. The vibration isolators 10 are coupled with a circular structural housing member 12, for example, a bearing housing, that houses a bearing assembly and a rotating member, for example, a rotor shaft (not shown), with the axis of rotation passing orthogonally through the intersection of the x- and y-axes. Each vibration isolator 10 is positioned exactly 120 degrees apart from one another along the circular structural housing member 12, as indicated by angles θ, thereby providing identical levels of vibration isolation and damping support in the x-direction and the y-direction to the structural housing member 12, and consequently the rotating member housed therein. Isotropic support systems, however, lack the ability to provide effective vibration isolation at the lowest frequencies that are typically associated with noise generation in the passenger cabin of an associated vehicle. Furthermore, isotropic support systems lack the ability to tune support with regard to expected directional accelerations in the system.